I don't know what model you are employing for the diode but nonetheless.
For (a) you should be able to preform a source transformation followed by a simple KVL to solve for the output voltage. You will have to assume that the diode is in a particular state, i.e. active or cutoff and further verify it's validity later on.
You can readily assume that the diode is on in the second case since nothing would prevent it from being forward biased.
In the first case it is easily verified the diode is on. If it were off, the entire 10mA would flow in the 2.2kΩ, making the voltage developed 22V in which case the diode would of necessity be turned on.
One would assume the Si diode has a typical forward bias on value of ~0.7V.